Coffee drinks are highly favored universally, and the so-called instant coffee drinks, which can be prepared from roasted and grounded beans or dried and granulated coffee extract, are widely consumed around the world. In Japan, meanwhile, packaged coffee drinks produced industrially tend to be favored as daily drinks, due to its unique culture. These drinks are made easy to drink before they are on the market, so that their flavor can continue to be significant.
Coffee drinks have such a long dietary history, and many researches have been made to ingredients contained in coffee, such as caffeine and chlorogenic acids. In particular chlorogenic acids were reported to have action of improving unidentified complaint syndrome such as total malaise and fatigue and easy fatigue caused by antihypertensive action or autonomic imbalance and improving function of vascular endothelial (e.g., Patent Documents 1 to 3).
Turning to commercially sold packaged coffee drinks, there are plenty of the brands thereof, ranging from weak coffee to rich coffee, including a black coffee type and a blended type containing sugar and milk. However, those products contain a relatively small amount of chlorogenic acid. Specifically, those products contain no more than 0.05 to 0.1 by mass of chlorogenic acid.
Most of the packaged coffee drinks recently on the market in Japan have a volume ranging from 190 to 300 g, and those having a volume of 190 g, among them, are increasingly in demand. Accordingly, drinks are required to contain chlorogenic acids in high concentrations, in order to include a sufficient amount of chlorogenic acids for significantly exhibiting a physiological effect thereof with a limited package volume.
Many methods of improving storage stability of packaged coffee drinks have been proposed so far. Examples thereof include a method producing coffee extract in which low molecular weight components such as formic acid, acetic acid and propionic acid are removed by adsorption by bringing into contact with a medium or weak basic anion exchange resin and a method in which a turbid substance in the form of fine particles is removed by bringing into contact with silica gel. However, both methods not only require additional equipment for production but also have a problem of apparent decrease in necessary flavor level after storing for a long period at high temperatures (e.g. Patent Documents 4, 5).
On the other hand, although there are a method in which a cellulose viscous substance is added, a treatment employing a mannan splitting enzyme and a method of removing precipitated components by adding acid, it turns out that such enzyme and acid treatments cause severely sour taste, thereby leading their natural taste to deteriorate (e.g. Patent Documents 6 to 8).
[Patent Document 1] JP-A-2002-53464
[Patent Document 2] JP-A-2002-145765
[Patent Document 3] JP-A-2003-261444
[Patent Document 4] JP-A-04-36148
[Patent Document 5] JP-A-04-360647
[Patent Document 6] JP-A-06-205641
[Patent Document 7] JP-A-07-184546
[Patent Document 8] JP-A-10-48819